Ch 14

Ch 14
The Lymphatic System
(The Immune System)
Ch 14
 4 types of common invaders that cause infection
and disease:
 1) viruses
 2) bacteria
 3) fungi
 4) parasites (certain protists)
 They are called PATHOGENS
Ch 14
 Viruses are technically non-living because
they lack cellular structure and exist only
within a host cell. They consist only of
nucleic acid and protein.
 The lymphatic system works after the
barriers of the integumentary system have
been compromised.
Ch 14
 4 components of the Lymphatic System:
1) Vessels
2) Fluid (lymph)
3) Lymphocytes (specialized cells for
defense)
4) Lymphoid tissues (lymphoid nodules)
and organs (tissue example: tonsils; organ
examples: lymph nodes, spleen, thymus)
Ch 14
 3 functions of LS:
 1) production, maintenance, and
distribution of lymphocytes
 2) the return of fluid and solutes from
peripheral tissues to the blood
 3) the distribution of hormones, nutrients,
and waste products from their tissues of
origin to the general circulation
Ch 14
 LYMPHATIC VESSELS (lymphatics):
 -they carry lymph from the peripheral tissue to
the venous system
 The smallest vessels are called Lymphatic
Capillaries. From there, lymph flows into larger
vessels that lead towards the trunk. (These walls
of these vessels are similar to veins; they also
have valves)
 They empty into 2 large Lymphatic ducts.
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 Lymphatic Ducts:
 The Thoracic Duct collects lymph from the lower
abdomen, pelvis, and lower limbs, and from the
left half of the head, neck, and chest.
 The smaller Right Lymphatic Duct delivers lymph
from the right side of the body above the
diaphragm. It empties into the right subclavial
vein.
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 LYMPHOCYTES: account for about 25% of
the circulating white blood cell population.
(Most lymphocytes are non-circulating=
found within lymphoid organs and tissues)
 3 classes of lymphocytes:
 1) T cells
 2) B cells
 3) NK cells
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 T Cells: (80% of circulating lymphocytes)
 Cytoxic T cells directly attack foreign cells or
body cells infected by viruses
 Helper T cells stimulate the activity of both T
cells and B cells
 Suppressor T cells inhibit both T cells and B cells
 (Helper and Suppressor T cells are called
REGULATORY T CELLS)
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 B Cells: (derived from bone marrow;
make up 10-15% of circulating
lymphocytes)
 B cells can differentiate into PLASMA
CELLS, which produce and secrete
antibodies (immunoglobins)
 Antibodies bind to specific targets called
antigens, which are usually pathogens.
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 NK Cells: (“natural killer cells”; remaining
5-10% of circulating lymphocytes)
 They attack foreign cells, normal cells
infected with viruses, and cancer cells that
appear in normal tissues.
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 Lymphocyte production and development is
called lymphopoiesis (occurs in the bone marrow
and thymus).
 During development in the bone marrow,
lymphoid stem cells are produced to carry on
one of two roles:
1) one group remains in the marrow to generate
B cells and NK cells
2) the other group migrates to the thymus to
produce T cells (thymosins control this)
Ch 14- Part 2
 Lymphoid Nodules- masses of lymphoid
tissue not surrounded by a fibrous
capsule; found beneath the epithelia lining
of various organs of the respiratory,
digestive, and urinary systems.
 The lymphocytes in a lymphoid nodule are
not always able to destroy bacterial or
viral invaders. (tonsillitis, appendicitis…)
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 Lymphoid Organs- separated from
surrounding tissues by a fibrous
connective-tissue capsule
1) Lymph nodes
2) Thymus
3) Spleen
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 Lymph nodes- they filter and purify the
lymph before it reaches the venous
system; they are small, oval organs that
can be up to 1 inch thick in diameter.
 Thymus- pink gland that lies posterior to
the sternum; site of T cell production
(thymosins control this process)
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 Spleen- adult spleen contains the largest
collection of lymphoid tissue in the body.
 It is about 5 in. long and is located to the left of
the stomach. (deep red in color)
 It function is similar to that of the lymph nodes,
but instead of filtering lymph, it filters blood. It
removes abnormal blood cells, and initiates the
responses of the T and B cells. It also stores iron
from recycled RBCs.
Ch 14
 LS has 2 roles: non-specific defenses and
specific defenses
 Non-Specific D: present at birth; responses are
the same regardless of the type of invading
agent; include physical barriers, immunological
surveillance, inflammation, and fever (NK cells)
 Specific D: protect against particular threats;
develop after birth (T and B cells)
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 2 types of immunity:
 1) Innate Immunity- genetically determined; born with
this (ex. Humans do not get sick with the same diseases
as goldfish)
 2) Acquired Immunity- arises by active or passive means
after birth.
 Active vs. Passive: active appears after exposure to an
antigen, resulting in an immune response (vaccine);
passive is produced by the transfer of antibodies to an
individual from another source. (rabies shot)
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 4 General Properties of Immunity:
 1) specificity
 2) versatility
 3) memory
 4) tolerance
 In an Immune Response, T cells are usually
activated before B cells
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 T cells divide into the following:
 Cytoxic T cells, Helper T cells, Memory T
cells, Suppressor T cells
(memory cells come from Helper T cells)
B cells also produce memory cells
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 5 classes of antibodies (Immunoglobins):
 IgG, IgM, IgA, IgE, IgD
 IgG is the largest and most diverse class
of antibodies (resist many viruses,
bacteria, and bacterial toxins)
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 Primary response if the initial response to
an antigen exposure.
 Secondary response reflects the presence
of large numbers of memory cells that are
already primed for the arrival of the
antigen.
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 Key hormones of the IS:
 Interleukins (IL), Interferons, Tumor Necrosis
Factors (TNFs)
 IL- most diverse and important messengers of
the IS; increase lymphocyte activity and
antibody production
 Interferons- released by infected cells to make
neighbors more resistant; attract NK cells; can
help some cancers
 TNFs- slow tumor growth and kill tumor cells
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 Immune Disorders:
 Autoimmune Disorders- immune response
mistakenly targets normal body cells and tissues
(rheumatoid arthritis)
 Immunodeficiency Diseases- the immune
response gets blocked some way (AIDS- helper
T cells are targeted for destruction)
 Allergies- inappropriate or excessive immune
responses to antigens
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 Aging and the IS:
 T cells become less responsive to antigens
 Number of helper T cells is reduced
 B cells are less responsive
 Immunological surveillance declines
(results in more cancers)
 More viruses and bacterial infections